It's all very simple - Public Domain, one and all. Knowing Koch it will probably be of the fine quality of their DVD of Repulsion, if you get my drift. If you don't get my drift, Repulsion was taken off a beat up 16mm print and was one of the sorriest-looking DVDs ever.
IF you want a good documentary on the Marx brothers, get "The Unknown Marx Brothers" (1993) dvd.
A very nice overview of the Marx brothers. Maybe the 5 disc set can serve as a supplement for the DVD, since it might have the full TV shows that are only highlighted on the documentary?